Information recording method and information recording apparatus for magneto-optic recording information medium

ABSTRACT

Methods and apparatuses are disclosed for improving accuracy of recording and reproducing information onto and from a magneto-optic recording information medium. In the first method, a width of a mark formed by a relatively low intensity light beam between two kinds of light beam intensities used for recording information is made larger than a sum of a track land width and the maximum track offset of the light beam, thereby the mark formed by the relatively low intensity light beam covers the track land portion in its full width. In the first apparatus, a reflected light beam from the magneto-optic recording information medium is split into a reflected beam for information reproducing and a reflected beam for tracking and focusing servos at the reproducing, thereby the apparatus can remove part being affected by the track groove portion from the reflected light beam for information reproducing. In the second method and apparatus, an intensity ratio of the two kinds of intensities of light beams used for information recording is controlled in such a manner that a mark width formed by the relative low intensity light beam is wider than a mark width formed by the relative high intensity light beam.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an information recording method for amagneto-optic recording information medium (magneto-optic disk) and amagneto-optic recording reproducing apparatus, and more particularly, tothe same for magneto-optic recording information medium having so-calledlight modulation overwriting function which enables one to directlywrite new information on old recorded information.

2. Description of Related Art

The inventors of this application have proposed a magneto-opticrecording information medium, namely, magneto-optic disk having lightmodulation overwriting function, and a magneto-optic recording apparatusin the Japanese Patent Application Laid-Open No. 1-119244 (1989).

The magneto-optic recording information medium and the magneto-opticrecording apparatus according to this invention are as follows.

"A magneto-optic recording information medium comprising a firstmagnetic layer having vertical magnetic anisotropy and a second magneticlayer laid on the first magnetic layer which has also vertical magneticanisotropy and is bonded to said first layer with exchange force,characterized in that: said second magnetic layer

(a) does not cause flux reversal and keeps its direction ofmagnetization constant at recording and producing,

(b) meets the requirement of Tc₁ <Tc₂

    ______________________________________                                        where                                                                         Tc.sub.1 Curie temperature of the first magnetic layer                        Tc.sub.2 Curie temperature of the second magnetic layer                       ______________________________________                                    

(c) meets the requirements of

    Hc.sub.1 >Hw.sub.1 +Hb, Hc.sub.2 >Hw.sub.2 +Hb

at room temperatures.

    ______________________________________                                        where                                                                         Hc.sub.1 coercive force of the first magnetic layer                           Hc.sub.2 coercive force of the record magnetic layer                          Hw.sub.1 shift quantity of inversion magnetic field due to                             exchange force of the first magnetic layer                           Hw.sub.2 shift quantity of inversion magnetic field due to                    Hb       applied magnetic field at recording (Hb > 0)                         ______________________________________                                    

"A magneto-optic recording apparatus comprising a magneto-opticrecording information medium having at least two magnetic layers withvertical magnetic anisotropy, one layer of which keeps its direction ofmagnetization constant and does not cause flux reversal at recording andreproducing, a beam emitting element which projects a beam on themagneto-optic recording information medium to record or reproduceinformation, and a magnetic field generator which generates a magneticfield to be applied to a portion of the magneto-optic recordinginformation medium projected by the beam emitting element with keepingthe direction of magnetic field constant."

Now, referring to the drawings, the explanation will be given in moredetail as follows.

FIG. 1(a) is a schematic diagram showing an outline of a magneto-opticrecording information medium and essential part of a magneto-opticrecording apparatus which records information on the medium and thesehave been proposed in the Japanese Patent Application Laid-Open No.1-119244 (1989) mentioned above. FIG. 1(b) is a partial section takenalong a circumference of the magneto-optic recording information mediumand also includes a graph showing a condition of a varying of laser beampower for information recording on the magneto-optic recordinginformation medium.

In FIG. 1(a) and (b), numeral 11 denotes a magneto-optic recordinginformation medium, 20, a laser beam from a laser beam emitting elementwhich projects the beam onto the magneto-optic recording informationmedium 11 to record or reproduce information, and 16, a beam spot whichis generated by condensing the laser beam 20 through an objective lens 5to be projected on the magneto-optic recording information medium 11.

Numeral 18 denotes a magnetic field generator which generates a magneticfield having a constant direction and being applied to a laser beamprojected portion on the magneto-optic recording information medium 11.

Numeral 2 denotes a substrate made of glass or plastics.

Numeral 13 denotes a first magnetic layer, which is laminated on thesubstrate 2 and has vertical magnetic anisotropy.

Numeral 14 denotes a second magnetic layer, which is laminated on thefirst magnetic layer 13 and has vertical magnetic anisotropy. The secondlayer 14 is bonded to the first magnetic layer 13 with exchange forceand does not exhibit flux reversal at recording or reproducing, thuskeeping the direction of magnetization constant.

Numeral 7 denotes an area with binary data "1" indicating that thedirection of magnetization of the first magnetic layer 13 is directedupward in FIG. 1(b).

The first magnetic layer 13 and the second magnetic layer 14 haverelations Tc₁ <Tc₂ (where Tc₁ and Tc₂ are Curie temperatures of thefirst and second magnetic layers 13 and 14 respectively) and Hc₁ >Hw₁+Hb, Hc₂ >Hw₂ +Hb (where Hc₁ and Hc₂ are coercive forces of the firstand the second magnetic layers 13 and 14 at a room temperature, Hw₁ andHw₂ are exchange bonding force of the first and the second magneticlayers 13 and 14 at a room temperature, and Hb is a magnetic fieldgenerated by the magnetic field generator 18) and are composed of rareearth metal-transition metal alloy.

In order to perform light modulation direct overwriting, it is necessaryto control the intensity of the laser beam 20 from the laser beamemitting element to three levels of high, intermediate and low. At thehigh level of the laser pulse beam the first magnetic layer forms eithera pit (mark) with upward direction of magnetization or a pit withdownward direction of magnetization and at the intermediate level of thelaser pulse beam, a pit is formed having the opposite magnetization.Reading of information can be performed with the low level laser beam.

Next, operation is described.

The magneto-optic recording information medium 11 is rotated in thedirection of an arrow a in the drawing. This medium 11 has two magneticlayers 13 and 14 as described above and is formed with a substrate 2,the first magnetic layer 13 and the second magnetic layer 14 in orderfrom the side of laser projection.

Now, the first magnetic layer 13 is a reading layer as well as arecording layer for holding magnetization orientation indicative ofinformation "0" or "1" and the second magnetic layer 14 is provided toeffect overwriting. This second magnetic layer 14 is called aninitialization layer and has both the functions of the conventionalauxiliary layer and the initialization magnet.

Characteristics of the first magnetic layer 13 and the second magneticlayer 14 are as follows:

Giving notations Tc₁ and Tc₂ to each Curie temperature of both thelayers, then

    Tc.sub.1 <Tc.sub.2.

Further, giving notations Hc₁ and Hc₂ to each coercive force of both thelayers, and notations Hwi (i=1, 2) to each exchange bonding force ofboth the layer, then

    Hc.sub.1 >Hw.sub.1 +Hb                                     (1)

    Hc.sub.2 >Hw.sub.2 +Hb                                     (2).

Inequality (1) holds good within the range of room temperatures to acertain temperature T₀ lower than Tc₁. That is, in the range of a roomtemperature to temperature T₀, the coercive force Hc₁ of the firstmagnetic layer 13 is greater than a sum of effect of exchange bondingforce Hw₁ and the applied magnetic field Hb at recording which isgenerated by the magnetic field generator 18 and is not affected by thedirection of magnetization of the second magnetic layer 14 and is ableto hold the direction of magnetization indicative of recordedinformation.

Inequality (2) holds good within the whole range of operatingtemperatures. That is, in the whole range of operating temperatures, thecoercive force Hc₂ of the second magnetic layer 14 is greater than a sumof effect of the exchange bonding force Hw₂ and the applied magneticfield Hb at recording which is generated by the magnetic field generator18. Therefore, once initializing the second magnetic layer 14 upward, ina strong magnetic field for example, giving the result as shown in FIG.1(b), the direction of magnetization is not reversed and the upwarddirection of magnetization is maintained throughout operation.

Explanation will first be given to the case of reproducing informationrecorded on the first magnetic layer 13.

As shown in FIG. 1(b), the first magnetic layer is magnetized upward ordownward in a domain corresponding to a binary code "1" or "0". Whenreproducing information, the beam spot 16 is projected on this firstmagnetic layer 13 and the direction of magnetization of this projectedarea of the first magnetic layer 13 is converted into opticalinformation with well-known optical Kerr effect and thus informationrecorded in the magneto-optic recording information medium 11 isdetected.

In this case, the intensity of the laser projected on the magneto-opticrecording information medium 11 is one at point A in a graph of FIG. 3described later. In the first and the second magnetic layers 13 and 14,the maximum temperature on the beam spot 16 projected by the light beamof this intensity does not reach respective Curie temperature Tc₁, Tc₂of both the layers. Therefore, magnetizing information is not eliminatedby beam projection of the beam spot 16.

A relation between temperatures and the inversion magnetic fields of thefirst magnetic layer 13 is shown in a graph of FIG. 2 and a relationbetween intensity of the laser beams on the magneto-optic recordinginformation medium 11 and temperature of the magnetic layers in thelaser spot is shown in the graph of FIG. 3. An inversion magnetic fieldis the minimum field required to reverse a direction of magnetizationand is expressed by

    Hc.sub.1 -Hw.sub.1.

When a laser intensity (power) R₁ is applied as shown in FIG. 1(b), arelation between inversion magnetic fields and temperatures of the firstmagnetic layer is shown in a solid line in FIG. 2 and when a laserintensity (power) R₀ is applied, the relation is shown in a broken line.

The recording operation is explained when information "0" is recorded,that is downward magnetization is given to the first magnetic layer 13.

When the laser beam 20 with intensity R₁ is projected, the temperatureof the first magnetic layer 13 in the beam spot 16 rises to Tr₁ in FIG.2. Then, when the disk is rotated and the laser beam 20 is not projectedon the beam spot 16, the temperature of the first magnetic layer 13falls. As can be seen from the solid line in FIG. 2, a followinginequality is valid within the range of room temperatures to Tc₁ :

    |Hb|>Hw.sub.1 -Hc.sub.1

Therefore, the direction of magnetization of the first magnetic layer 13is the direction of the magnetic field generated by the magnetic fieldgenerator 18, that is, the direction of a biasing magnetic field Hb,namely downward direction.

The recording operation is then explained when information "1" isrecorded, that is, upward direction of magnetization is given to thefirst magnetic layer 13.

When the laser beam with its intensity R₀ is projected, the temperatureof the first magnetic layer 13 in the beam spot 16 rises to Tr₀ in FIG.2. Then, when the disk is rotated and the laser beam 20 is not projectedon the beam spot 16, the temperature of the first magnetic layer 13falls. As can be seen from the broken line in FIG. 2, a followinginequality is valid in the vicinity of the temperature Tp:

    |Hb|<Hw.sub.1 -Hc.sub.1.

Therefore, the direction of magnetization of the first magnetic layer 13is the direction in which the exchange force acts, that is, thedirection of magnetization of the second magnetic layer 14, namelyupward direction.

Then, when overwriting is performed by the above operation, the laserbeam is intensity-modulated to become R₁ or R₀ that is the intensity atpoint C or B in FIG. 3 according to the binary code "0" or "1" ofinformation, thus the overwriting can be effected on old data in realtime without necessity of magnets for initializing.

The laser intensity at point A in FIG. 3 is the intensity used forreading information as mentioned above. Using this intensity at point A,the maximum temperatures of the first and the second magnetic layers 13and 14 in the beam spot 16 do not reach respective Curie temperature Tc₁and Tc₂ of both the layers. Therefore, direction of magnetization,namely, recorded information is not eliminated by beam projection on thebeam spot 16.

Now, the reason is explained why the curve of temperatures of inversionmagnetic fields in the first magnetic layer 13 separates into the brokenline curve and the solid one according to the laser intensities R₀ or R₁as shown in FIG. 2.

Both the magnetic layers 13 and 14 exhibit a temperature rise due tolaser projection. The first layer 13 has a higher heat radiation ratethan that of the second layer 14. The reasons are as follows.

(i) Because the laser beam 20 is projected from the side of the firstmagnetic layer 13, the maximum reachable temperature of the first layer13 is higher than that of the second layer 14 and thus the heatradiation rate of the first layer 13 is higher than that of the secondlayer 14.

(ii) The first magnetic layer 13 is adjacent to the substrate 2 andradiates heat through the substrate 2.

(iii) Thickness of the first magnetic layer 13 is very thin, thereforeheat radiation is great.

Thus, the heat radiation rate of the first magnetic layer 13 is higherthan that of the second magnetic layer 14. Due to projection of thelaser beam 20 with its intensity R₀, the temperature of the firstmagnetic layer 13 rises to Tr₀ in FIG. 2 and after that drops to aroundTp in FIG. 2. At this time, the temperature of the second magnetic layer14 is denoted T₂ r₀. Due to projection of the laser beam 20 with itsintensity R₁, the temperature of the first magnetic layer 13 rises toTr₁ in FIG. 2 and thereafter the temperature of the first magnetic layer13 drops to around Tp in FIG. 2. At this time the temperature of thesecond magnetic layer 14 is denoted T₂ r₁, then due to differencebetween the heat radiation rates mentioned above,

    T.sub.2 r.sub.0 <T.sub.2 r.sub.1

results.

That is, when the laser beam 20 with its higher intensity R₁ isprojected, the temperature of the second magnetic layer 14 becomeshigher when the temperature of the layer 13 is about Tp. Consideringthat the exchange bonding force has a tendency to decrease as thetemperature of the magnetic layer becomes high, the exchange bondingforce becomes small when the laser beam 20 with its higher intensity R₁is projected. Therefore, the difference in FIG. 2 arises between thesolid line and the broken line curves of the temperature varying ofinversion magnetic fields of the first magnetic layer 13. This causesmagnetization hysteresis in relation to temperature and enablesoverwriting.

Ex. 1

The magneto-optic recording information medium 11 is formed bylaminating in order ferromagnetic substances, for example,

first magnetic layer 13: Tb₂₃ Fe₇₂ Co₅ (thickness 500Å) and

second magnetic layer 14: Gd₁₄ Tb₁₄ Co₇₂ (thickness 1500Å) on a glasssubstrate 2 by the sputtering method, for example, and the magneticlayers are bonded together by exchange force.

Curie temperature of the first magnetic layer 13 is about 180° C., andthe second magnetic layer 14 has an inversion magnetic field of 1 k Oewithin the range of room temperatures to 250° C. and does not exhibitflux reversal within the range of operating temperatures. In the firstmagnetic layer 13, the exchange force becomes greater than coerciveforce at about 150° C. The greatest difference between the exchangeforce and the coercive force is equivalent to a magnetic field of about1 k Oe.

The magnetic field generator 18 is always producing a magnetic field ofabout 1 k Oe in a constant direction. The magneto-optic recordinginformation medium 11 is exposed to a magnetic field stronger than theinversion magnetic field of the second magnetic layer 14 and thus thelayer 14 is initially once magnetized, for example, upward anduniformly. At this time a direction of a magnetic field generated by themagnetic field generator 18 is upward and the first and the secondmagnetic layers 13 and 14 have the relation mentioned above.

In the magneto-optic recording information medium 11 thus constituted,owing to the above mentioned operations light modulation directoverwriting can be effected by modulating only a laser beam intensity.

Practically, signals with a linear velocity of 6 m/sec and pit length of0.8 through 5 μm were light-modulated on the condition that the magneticfield generated by the magnetic field generator 18 is 1000 Oe; laserpeak power is 16 mW; bottom power is 5 mW. Then an erase ratio of morethan 25 dB was obtained. Reproducing was performed with laser power of1.5 mW.

Exs. 2 through 8

There is no problem when the coercive force of the second magnetic layer14 is sufficiently large at around Curie temperature of the firstmagnetic layer 13, and both the magnetic layers 13 and 14 were laminatedon a glass substrate 2 by the sputtering method. Thus various types ofmagneto-optic recording information mediums were obtained as shown inTable 1 in the same as "Ex. 1".

                  TABLE 1                                                         ______________________________________                                        Ex.    1st magnetic layer                                                                            2nd magnetic layer                                     ______________________________________                                        2      Tb.sub.23 Fe.sub.72 Co.sub.5 500Å                                                         Gd.sub.15 Tb.sub.14 Co.sub.71                                                             1500Å                                  3      Tb.sub.23 Fe.sub.72 Co.sub.5 400Å                                                         Gd.sub.14 Tb.sub.14 Co.sub.72                                                             1500Å                                  4      Tb.sub.23 Fe.sub.72 Co.sub.5 400Å                                                         Gd.sub.14 Tb.sub.16 Co.sub.70                                                             1500Å                                  5      Tb.sub.23 Fe.sub.72 Co.sub.5 500Å                                                         Gd.sub.14 Tb.sub.14 Co.sub.72                                                             1800Å                                  6      Tb.sub.23 Fe.sub.72 Co.sub.5 400Å                                                         Gd.sub.14 Tb.sub.14 Co.sub.72                                                             1800Å                                  7      Tb.sub.23 Fe.sub.72 Co.sub.5 500Å                                                         Tb.sub.30 Co.sub.70                                                                       1500Å                                  8      Tb.sub.23 Fe.sub.72 Co.sub.5 500Å                                                         Tb.sub.33 Co.sub.65                                                                       1500Å                                  ______________________________________                                    

Using each magneto-optic recording information medium shown in Table 1and a linear velocity of 6 m/sec, erase ratios more than 20 dB and 23through 35 dB at the optimum power were obtained in the same way as "Ex.1" except that the light modulation was performed as shown in Table 2,and thus the same light modulation direct overwriting as "Ex. 1" couldbe effected.

                  TABLE 2                                                         ______________________________________                                              generated mag-                                                                             peak power   bottom power                                  Ex.   netic field/Oe                                                                             /mW          /mW                                           ______________________________________                                        2     1000 ± 100                                                                              12.0 through 17.0                                                                          4.0 through 7.0                               3     1200 ± 100                                                                              10.0 through 15.0                                                                          4.0 through 7.0                               4     1300 ± 100                                                                              11.0 through 17.0                                                                          4.0 through 7.0                               5     1000 ± 100                                                                              13.0 through 17.0                                                                          4.5 through 7.5                               6     1200 ± 100                                                                              12.0 through 15.0                                                                          4.5 through 7.5                               7      800 ± 100                                                                               9.0 through 17.0                                                                          3.5 through 7.5                               8     1200 ± 100                                                                              12.0 through 17.0                                                                          4.0 through 8.0                               ______________________________________                                    

Ex. 9

As for other types of magneto-optic recording information mediums,ferromagnetic amorphous alloys of transition metals and rare earthmetals are suitable. For example, by using compositions and layerthickness of

first magnetic layer: Tb₂₃ Fe₆₇ Co₁₀ (thickness 500 Å) and

second magnetic layer: Gd₁₂ Tb₁₂ Co₇₆ (thickness 1500 Å)

good overwriting can be effected in the same as "Ex. 1".

Further, each magnetic layer may be formed of ferromagnetic substancessuch as DyFeCo, TbCo, TbFe/GdCo, GdDyCo, TbDyCo, DyCo. Other magneticlayers which do not interfere with the first and the second layers 13and 14 in operations at about room temperatures may be contained in themagneto-optic recording information medium. In this case the secondmagnetic layer 14 does not exhibit flux reversal in the operating range.In addition a dielectric layer may be contained in the medium 11 toimprove signal quality or to reduce oxidation corrosion of the magneticlayer.

FIG. 4(a) is a schematic diagram showing an optical system configurationof the abovementioned magneto-optic recording apparatuses.

In this figure, numeral 11 denotes the abovementioned magneto-opticrecording information medium. A laser beam 20 emitted from a laser beamemitting element 31 is projected on the magneto-optic recordinginformation medium 11 through a collimator lens 32, a beam splitter 33,and an objective lens 34.

The laser beam 20 is reflected at the medium 11 and this reflected beampasses to the beam splitter 33 through the objective lens 34 and therethe traveling direction of the beam is changed by 90°. Then, this turnedbeam passes to a tracking servo detector 37 through a half-wave plate 35and a beam splitter 36 and at the same time part of the turned beam isagain turned by 90° at the beam splitter 36 and passes to a focusingservo detector 39 through a condenser lens 38.

FIG. 4(b) is a schematic diagram showing a circuit configuration fortaking out reproduced signals from the magneto-optic recordinginformation medium 11 by using the above-mentioned optical system.

In this figure, detected signals of the tracking servo detector 37 areinputted at a (-) terminal of an operational amplifier 40 and detectedsignals of the focusing servo detector 39 are inputted at a (+) terminalof the operational amplifier 40. An output of this operational amplifier40 is the reproduced signal.

Now, information is practically recorded on the magneto-optic recordinginformation medium 11 along a concentric circular or spiral track on itas is omitted in FIG. 1(a).

FIG. 5 is a schematic plan view showing a track configuration. The trackis configured of a convex land portion 52 on its middle and grooveportions 51 elongated on both sides of the land portion 52. The landportion 52 of each track is side by side with a next land portion 52,but with interposed groove portions 51.

When information is recorded on such a track on the magneto-opticrecording information medium 11, laser beams with two kinds ofintensities R₀ and R₁ are used. When recorded with high output (highpower) of the intensity R₁, a high power mark 53 formed on the track ofthe magneto-optic recording information medium 11 (shown with "H" inFIG. 5) is enlarged in a radial direction of the medium 11 (upward anddownward in the figure) due to thermal diffusion.

On the other hand, when recorded with low output (low power) of theintensity R₀, a low power mark 54 formed on the track of the medium 11as shown with "L" is not so enlarged in a radial direction of the medium11.

FIG. 6 shows a state in which the low power mark 54 is overwritten onthe high power mark 53 once recorded, in other words, the high powermark 53 is erased. That is, when the low power mark 54 is overwritten onthe high power mark 53 that has pushed out portions on both the grooveportions 51 on both sides of the land portion 52, unerased portions 55of the high power mark 53 remain on both sides of the land portion 52and on both the groove portions 51. A length between two arrows denotedwith reference numeral 56 indicates the width of the low power mark 54.

As shown in FIG. 6, when the unerased portions 55 of the high power mark53 remain in a large area on the land portion 52, practically,information corresponding to the low power mark 54 may be deemed to havebeen recorded, nevertheless, information of the magneto-optic recordinginformation medium 11 might be read as if information corresponding tothe high power mark 53 were recorded due to the effect of the unerasedportions 55.

The reason why these unerased portions 55 remain is as follows.

In the conventional magneto-optic recording apparatus, one laser beamwith high intensity R₁ and the other laser beam with low intensity R₀are used for information recording. These intensities are usually fixedand the ratio of both the intensities is a constant value depending on aapparatus. Then, a relation between projected beam intensitydistribution and temperature rise area by heating is shown in FIG. 7 andFIG. 8.

When a signal to be recorded is "1", the beam intensity is brought tothe high intensity R₁ as shown in FIG. 7. On an area A₁ heated by lightbeams with intensities more than the high intensity R₁, informationcorresponding to a signal "1" (high power mark 53) is recorded. On anarea A₀ heated by light beams with intensities between the highintensity R₁ and the low intensity R₀, information corresponding to asignal "0" (low power mark 54) is recorded. The low power mark 54corresponding to a signal "0" is recorded, in other words, this meansthat when the high power mark 53 corresponding to a signal "1" has beenalready recorded, this information is erased. Further, on an area A_(i)heated by light beams with intensities less than the low intensity R₀,information is neither recorded nor erased, that is, neither the highpower mark 53 nor the low power mark 54 is recorded and a former stateis maintained.

When a signal to be recorded is "0", the beam intensity is brought tothe low intensity R₀ as shown in FIG. 8. On an area A_(o) ' heated bylight beams with intensities more than the low intensity R₀, informationcorresponding to a signal "0" (low power mark 54) is recorded.Information corresponding to a signal "0" is recorded, in other words,this means that when the high power mark 53 for a signal "1" has beenalready recorded, this information is erased. On an area A_(i) ' heatedby light beams with intensities less than the low intensity R₀,information is neither recorded nor erased, that is, neither the highpower mark 53 nor the low power mark 54 is recorded and a former stateis maintained.

As can be seen from the foregoing, the high power mark 53 for a signal"1" has already been recorded on a track and thereafter when the lowpower mark 54 for a signal "0" is overwritten on this track, in the casewhere the area A₁ indicating the high power mark 53 in FIG. 7 is greaterthan the area A₀ ' indicating the low power mark 54 in FIG. 8, the highpower mark 53 previously recorded is not completely erased and unerasedportions remain.

Now, the schematic diagram in FIG. 6 shows that both centers of the highpower mark 53 and the low power mark 54 overwritten on the former are onthe center line of the land portion 52, that is, track offset, which iscontrol error for displacement to the track (land portion 52) centerline, is "0".

FIG. 9 is a schematic diagram showing that the above-mentioned trackoffset is not "0". In the figure, the high power mark 53 is recordedwith the track offset "0", but the low power mark 54 overwritten on theformer is recorded on the land portion 52 with the track offset of awidth denoted with a reference numeral 59. That is, a two-dot brokenline denoted with reference numeral 58 is the track center line (alsocenter line of the land portion 52) and a one-dot broken line denotedwith reference numeral 57 is a center line of the low power mark 54 anda distance between both the lines is the track offset 59.

Now, when the track offset 59 exceeds a certain value, the unerasedportion 55 of the high power mark 53 remains in a large area on the landportion 52 after the high power mark 53 was erased by the low power mark54. FIG. 9 is a schematic diagram showing such a state, wherein the lowpower mark 54 is greatly downward offset and thus the upper unerasedportion 55 remains in a large area on the land portion 52 in thedrawing.

As shown in FIG. 9, when the unerased portion 55 of the high power mark53 remains in a large area on the land portion 52, practicallyinformation corresponding to the low power mark 54 may be assumed tohave been recorded, nevertheless, information of the magneto-opticrecording information medium 11 might be read as if informationcorresponding to the high power mark 53 were recorded due to the effectof the unerased portion 55.

As mentioned above, in the conventional methods of information recordingon the magneto-optic recording information medium and the magneto-opticrecording apparatuses, two kinds of light beams are used and theintensity of each beam is fixed, in addition the track offset arises,thus the high power mark corresponding to a signal "1" is not completelyerased and the unerased portion remains. Thus there is a problem of howto completely erase the high power mark.

SUMMARY OF THE INVENTION

This invention is attained in view of this circumstances and it is aprincipal object of the present invention to provide a method ofinformation recording onto a magneto-optic recording information mediumand a magneto-optic recording apparatus which are capable of avoidingmisrecognition of signals caused by an unerased high power mark portiongenerated when a low power mark for a signal "0" is overwritten on ahigh power mark for a signal "1".

Among the information recording methods for the magneto-optic recordinginformation medium according to the invention, in the first invention, awidth of the mark formed by a low intensity light beam between two kindsof light beams of different intensities is brought to a width more thansum of the track land width and the maximum error for light beamposition control to the track center line, that is, the maximum trackoffset. Information is overwritten under this condition. Thereby, in thecase where the track offset arises, the mark recorded by the lowintensity light beam covers the whole track land portion, thus thepreviously recorded mark is perfectly overwritten and no unerasedportion remains.

Among the methods of the invention, in the second invention, a beamintensity ratio of the two kinds of beam intensities used forinformation recording is made variable, thereby when the light beam iscontrolled in such a way that a heated area generated by the lowintensity light beam is larger than a heated area generated by the highintensity light beam, the previously recorded mark is perfectlyoverwritten and thus, no unerased portion remains.

Further, among the magneto-optic recording apparatuses according to theinvention, the apparatus of the first invention is provided with meansfor splitting a reflected beam from the magneto-optic recordinginformation medium into a reflected beam for reproducing information anda reflected beam for tracking servo and means for removing part, whichis affected by the groove portions, of the former. In this case, theremoval is effected on a light path of the reflected beam or on a lightreception surface of a reproduced signal detector. By this means,following the track is performed as same as in the conventional mannerand the part affected by the groove portions of the reflected beam forreproducing information is removed, thus information can be correctlyread and accuracy of the reproduced signals is improved.

Further, among the magneto-optic recording apparatuses of the inventionan apparatus of the second invention is provided with means for varyingan intensity ratio of two kinds of beam intensities beams used forrecording information. By using this means when the two beams arecontrolled in such a manner that the heated area of the track generatedby the low intensity beam is larger than the heated area generated bythe high intensity beam, a previously recorded mark is perfectlyoverwritten and no unerased portion remains.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic diagram showing an essential part of aconventional magneto-optic recording information medium and itsinformation reading apparatus,

FIG. 1(b) is a partial section taken along a circumference of theconventional magneto-optic recording information medium and alsoincludes a graph showing a condition of change in laser beam power forinformation recording on the medium,

FIG. 2 is a graph showing a relation between inversion magnetic fieldsand temperatures in the first magnetic layer of the magneto-opticrecording information medium according to this invention,

FIG. 3 is a graph showing relations between the laser beam intensitiesand temperatures of magnetic layer in the laser spot on themagneto-optic recording information medium,

FIG. 4(a) is a schematic diagram showing an optical system configurationof the conventional magneto-optic recording apparatus,

FIG. 4(b) is a schematic diagram showing a configuration of aconventional signal reproducing system,

FIG. 5 is a schematic diagram showing a state of information recordingon a track of the magneto-optic recording information medium by usingthe high power mark and low power mark,

FIG. 6 is a schematic diagram showing that the low power mark isoverwritten on the high power mark,

FIG. 7 and FIG. 8 are graphs and schematic diagram showing a relationbetween the light beam intensity distribution and the heated areathereby when the light beam is projected on the magneto-optic recordinginformation medium by using the conventional method and apparatus,

FIG. 9 is a schematic diagram showing a state of the track offset beingnot "0" when the conventional information recording method for themedium is used,

FIG. 10 and FIG. 11 are schematic diagrams explaining the methods of theinvention, in which FIG. 10 shows a state of the track offset being "0",and FIG. 11 a state of the track offset being maximum,

FIG. 12(a) is a schematic diagram showing an optical systemconfiguration of a magneto-optic recording reproducing apparatusaccording to the first invention,

FIG. 12(b) is a schematic diagram showing a signal reproducing systemconfiguration of the above apparatus,

FIG. 13 is a schematic diagram showing a configuration of a slit (lightreception surface of the reproduced signal detector) disposed on anoptical path of the optical system of FIG. 12(a),

FIG. 14 is a schematic diagram showing a configuration of a lightreception surface of the reproduced signal detector,

FIGS. 15(a) and 15(b) are a graph and a schematic diagram showing arelation between the light beam intensity distribution and the heatedarea thereby when the light beam is projected on the magneto-opticrecording information medium by using the method and apparatus of thesecond invention,

FIG. 16 is a block diagram showing one example of a configuration of themagneto-optic recording apparatus of the second invention,

FIG. 17 is a schematic side section diagram showing a magneto-opticrecording information medium having four magnetic layers which is usedfor other embodiment of the inventions, and

FIGS. 18(a) and 18(b) are an explanatory view showing change force amongthe magnetic layers of FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the invention will be described in detail referringto the drawings.

FIG. 10 is a schematic diagram showing a state of information recordingusing the method of the first invention among the information recordingmethods for the magneto-optic recording information medium according tothe invention.

In this figure, the recording width of the low power mark 54 on thetrack is set to become wider than sum of the width of the land portion52 and the maximum track offset 59. In this case, the width of the highpower mark 53 is made wider than that shown in FIG. 5, but this is not aproblem as long as the high power mark 53 is within the groove portions51 on both sides of the land portion 52.

In FIG. 10, a state is shown in which the low power mark 54 isoverwritten on the high power mark 53 with the track offset 59 being 0.In this case, the low power mark 54 is protruded by a half of themaximum track offset to each groove portion 51 on both sides of the landportion 52. Thus, at reading information, misreproducing can not begenerated because no unerased portion 55 exists on the track landportion 52.

FIG. 11 shows a state in which the low power mark 54 is overwritten onthe high power mark 53 with the track offset 59 being maximum. In thiscase, the low power mark 54 protrudes with equal to the maximum trackoffset to one of the groove portions 51 on one side of the land portion52, but retracts to just a boundary between the land portion 52 and theother groove portion 51. Thus, at reading information, reproducing ofthe high power mark can not be caused because no unerased portion 55exists on the track land portion 52.

Now, the apparatus of the first invention will be described in detailbased on the drawings of its embodiment.

FIG. 12(a) is a schematic diagram showing an optical systemconfiguration of the magneto-optic recording reproducing apparatusaccording to the first invention.

In this figure, numeral 11 denotes the above magneto-optic recordinginformation medium, a laser beam 20 emitted from a beam emitting element31 is projected on the medium 11 through a collimator lens 32, a beamsplitter 33, and an objective lens 34.

The laser beam 20 is reflected at the magneto-optic recordinginformation medium 11 and passes to the beam splitter 33 through theobjective lens 34 and there its traveling direction is turned by 90° andthe beam passes to a tracking servo detector 37 through a half-waveplate 35, a beam splitter 41, and a beam splitter 36. At the same time,the direction of part of the beam is turned by 90° at the beam splitter36 and this beam passes to a focusing servo detector 39 through acondenser lens 38.

On the other hand, the traveling direction of part of the beam is turnedby 90° at the beam splitter 41 and the beam passes to a beam splitter 43through a slit 42 and there, is split into two directions and projectedon reproduced signal detectors 44 and 45 respectively.

That is, in the magneto-optic recording apparatuses of the firstinvention, the optical system has the conventional configuration andfurther includes the beam splitter 41 between the beam splitters 33 and36. As mentioned above, the beam splitter 33 changes the direction ofthe reflected beam from the magneto-optic recording information medium11 and the beam splitter 36 splits the reflected beam, whose directionis changed by the splitter 33, into a beam for the tracking servodetector 37 and a beam for the focusing servo detector 39. Thus by usingthis beam splitter 41, part of the reflected beam from the magneto-opticrecording information medium 11 is taken out to be projected onto thereproduced signal detectors 44 and 45 through the slit 42 and the beamsplitter 43.

FIG. 12(b) is a schematic diagram showing a system configuration fortaking out the reproduced signals from the medium 11 with the opticalsystem of the apparatus of the first invention.

In this configuration, detected signals of the reproduced signaldetector 44 are inputted at a (-) terminal of an operational amplifier40 and detected signals of the reproduced signal detector 45 areinputted at a (+) terminal and an output of the operational amplifier 40is the reproduced signal.

Now, in the optical system of the magneto-optic recording apparatus ofthe first invention, the slit 42 is interposed between the beamsplitters 41 and 43. This slit 42 is so formed that it curves both sidesof the width of the reflected beam from the medium 11 as shown in theschematic diagram of FIG. 13. More particularly, hatched portions of theslit 42 in FIG. 13 are light shield portions.

By interposing the slit 42 having such shape on an optical path betweenthe beam splitter 41 and the reproduced signal detectors 44, 45, thesystem can remove parts 62 and 63 of the reflected beam from the grooveportions 51 which are affected by the unerased portions 55 generatedwhen the low power mark 54 is overwritten on the high power mark 53 asshown in FIG. 10, thus the system can project onto the reproduced signaldetectors 44 and 45 only part 61 of the reflected beam indicative ofcorrect information.

Further, in the above embodiment, the slit 42 is placed on a branchedlight path toward the detector 45 after the reflected beam from themedium 11 is split at the splitter 41 from the direction of the trackingservo detector 37 or the focusing servo detector 39, but as analternative a configuration shown in FIG. 14 is usable. That is, thelight reception surface of each reproduced signal detector 44, 45 iscomprised of an incident light detective surface 66 and light shieldnon-sensitive portions 65. In this case, it is needless to say that thenon-sensitive portion 65 corresponds to the reflected beam part affectedby the unerased portions 55 shown in FIG. 10.

Needless to say, it is possible to apply the configuration such as theslit 42 of FIG. 13 rather than the shape of FIG. 14 as the lightreception surface of the reproduced signal detector 44 or 45 and a shapeis also usable which is made by linearly narrowing a portion of thelight reception surface corresponding to both edges of the track.

FIG. 15(a) is a graph for explaining the principle of the informationrecording method for the magneto-optic recording information medium andthe information recording apparatus according to the second invention.

When a signal "1" is recorded on the magneto-optic recording informationmedium 11, the beam intensity is so controlled that it conforms to acurve Q₁ of FIG. 15(a), thereby an area A₁ heated by intensities morethan the high intensity R₁ has a diameter W₁ shown with hatching. Thisarea A₁ becomes the high power mark 53.

On the other hand, when a signal "0" is recorded, the beam intensity wasformerly so controlled that it conforms to a curve Q₂ shown with abroken line, and the low power mark 54 with a diameter W₁ was recordedon the track. However, in the present invention, when a signal "0" isrecorded, the beam intensity is so controlled that it conforms to acurve Q₃ stronger than the curve Q₂, thereby a diameter of an area A₀heated by intensities stronger than the low intensity R₀ becomes W₂increasing larger than W₁. This area A₀ becomes the low power mark 54.

As mentioned above, when the low power mark 54 is recorded in responseto a signal "0" onto the high power mark 53 already recorded in responseto a signal "1" with controlling the beam intensity, the diameter W₂ ofthe low power mark 54 is larger than the diameter W₁ of the high powermark 53, thus the high power mark 53 is perfectly overwritten by the lowpower mark 54, that is, erased.

In addition, in FIG. 15, instead of controlling the curve Q₂ low powerbeam intensity in such a manner that is conforms to the curve Q₃ insteadof the curve Q₂, the curve Q₁ high power beam intensity may be socontrolled that it conforms to the curve Q₄ which is shown in a one-dotbroken line and reduced somewhat in its intensity from the curve Q₁. Thesame effect as the former is obtained.

FIG. 16 is a block diagram showing essential part of the magneto-opticrecording apparatus of the second invention based on the aboveprinciple.

In FIG. 16, reference numeral 101 denotes a light modulation portion, towhich a recording signal RD of "1" or "0", which is to be recorded onthe magneto-optic recording information medium 11, is inputted. Thislight modulation portion 101 generates signals for modulating a lightbeam in response to the inputted recording signal RD and gives themodulated signals to a beam intensity control portion 102.

The beam intensity control portion 102 generates signals for controllingthe beam intensity in response to signals inputted from the lightmodulation portion 101 and gives them to a semiconductor laser 31 of alight beam emitting element.

Further, control signals outputted from a CPU 104 is given to the beamintensity control portion 102. As shown in FIG. 15, when the low powermark 54 is recorded on the magneto-optic recording information medium 11in response to a signal "0", the CPU 104 controls the original beamintensity of the curve Q₂ in FIG. 15 in such a manner that it conformsto the curve Q₃. This control is executed in response to externalcommand signal So given to the CPU 104.

By using the magneto-optic recording apparatus according to the secondinvention, the unerased portion of the high power mark 53 does notremain when overwritten by the low power mark 54, thus accuracy ofinformation recording and reproducing is improved.

Further, in the above embodiments, the high power mark 53 is recorded inresponse to a signal "1", and the low power mark 54 is recorded inresponse to a signal "0", but recording in such a manner is alsopossible that the low power mark 54 is recorded in response to a signal"1" and the high power mark 53 is recorded in response to a signal "0"on the magneto-optic recording information medium 11.

As mentioned above in detail, according to the first invention of theinformation recording methods for the magneto-optic recordinginformation medium, when the low power mark is overwritten onto the highpower mark already recorded, the unerased portion does not remain on theland portion, thereby generating no information misreproducing.

In addition, according to the first invention of the informationrecording apparatus, when information with the low power mark isoverwritten onto information with the high power mark already recordedon a track of the magneto-optic recording information medium, effect ofthe unerased portion contained in the reflected beam from the track canbe eliminated.

Still further, according to the second invention of the informationrecording methods for the magneto-optic recording information medium andto the second invention of the information recording apparatus, wheninformation with the low power mark is overwritten onto information withthe high power mark already recorded on a track of the magneto-opticrecording information medium, the effect of the unerased portioncontained in the reflected beam from the track can be eliminated.

Now, each of the above inventions is explained for the magneto-opticrecording information medium 11 having two magnetic layers, and this isfor simplification of explanation, but each of the above inventions canalso be applied to the medium 11 having three or more magnetic layers. Amagneto-optic recording information medium 11 having four magneticlayers shown in FIG. 17 will be explained as one example.

This medium 11 is formed with lamination of a dielectric layer 81 madeon, for example, a glass substrate 2 by the sputtering method forexample, a first magnetic layer 13 as a recording layer, a secondmagnetic layer 14 as an auxiliary layer for recording, a third magneticlayer 83 as a control layer, a fourth magnetic layer 84 as aninitialization layer, and a protective layer 82 in order.

Material and thickness of each layer are as follows:

    ______________________________________                                        dielectric layer (81)                                                                          SiNx         65 nm                                           1st magnetic layer (13)                                                                        Tb.sub.22 Fe.sub.69 Co.sub.9                                                               80 nm                                           2nd manetic layer (14)                                                                         Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                     150 nm                                          3rd manetic layer (83)                                                                         Tb.sub.30 Fe.sub.84                                                                        20 nm                                           4th magnetic layer (84)                                                                        Tb.sub.30 Co.sub.70                                                                        40 nm                                           protective layer (82)                                                                          SiNx         70 nm                                           ______________________________________                                    

Characteristics of these magnetic layers 13, 14, 83, 84 are as follows:

Each adjacent magnetic layers are bonded with exchange force.

The first magnetic layer 13 effects information recording and holding.

The second magnetic layer 14, the third magnetic layer 83, and thefourth magnetic layer 84 do not effect as information media and they areadded to enable light modulation direct overwriting. The fourth magneticlayer 84 is an initialization layer which does not cause flux reversalof sublattice against temperature rise with laser beam projection withinthe range of operation and have an effect of opposing a bias magneticfield generated by the magnetic field generator 18.

The third magnetic layer 83 is a control layer which cuts off exchangeforce coming from the fourth magnetic layer 84 at high temperatures.

Denoting Curie temperature of i-th magnetic layer with Tci; halfmagnetic field width of an inversion magnetic field (corresponds tocoercive force) in the i-th magnetic layer with Hci; exchange forcewhich the i-th magnetic layer receives from adjacent magnetic layerswith Hwi, the magnetic characteristics of the magnetic layers 13, 14, 83and 84 are as following inequalities (a) through e(g):

In addition, the exchange force is a transition width of the i-thmagnetic layer and as to the second magnetic layer 14 and the thirdmagnetic layer 83, it is defined for flux reversal as shown in FIGS.18(a) and 18(b).

    ______________________________________                                        Tc.sub.4 > (Tcomp.sub.4) > Tc.sub.2 > Tc.sub.1 > (Tcomp.sub.2)                             > Tc.sub.3 room temperature. . .(a)                              1st magnetic layer                                                                         Hw.sub.1 < Hc.sub.1 ; to room temperature. . .(b)                             Hw.sub.1 > Hc.sub.1 ; to Tc.sub.1 . . .(c)                       2nd magnetic layer                                                                         Hw.sub.2 > Hc.sub.2 ; to Tc.sub.3 . . .(d)                                    Hw.sub.2 < Hc.sub.2 ; to Tc.sub.1 . . .(e)                       3rd magnetic layer                                                                         Hw.sub.3 > Hc.sub.3 ; to Tc.sub.3 . . .(f)                       4th magnetic layer                                                                         Hw.sub.4 < Hc.sub.4 ; within the range of opera-                              ting temperature. . .(g)                                         ______________________________________                                    

The inequality (b) shows that magnetization of the first magnetic layer13 does not reverse regardless of flux reversal of the second magneticlayer 14 at room temperatures, (d), (f), and (g) show that direction ofmagnetizations of the second magnetic layer 14, third magnetic layer 83and fourth magnetic layer 84 are all downward (direction of theprotective layer 82) at room temperatures after recording.

When the information recording methods for the magneto-optic recordinginformation medium 11 according to the invention is effected using thismedium having four magnetic layers, the unerased portion is perfectlyeliminated and the system enables stable recording and reproducing ascompared with the fact that when the medium having two magnetic layersis used, the unerased portion caused by beam spot displacement and beamintensity (laser power) fluctuation may greatly impair the reproducedsignals.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within themeter and bounds of the claims, or equivalents of such meter and boundsthereof are therefore intended to be embraced by the claims.

What is claimed is:
 1. An information recording method for amagneto-optic recording information medium comprising the stepsof:providing on the magneto-optic recording information medium a trackhaving a land portion, said land portion for carrying the two kinds ofinformation, and said land portion having edges defining groove portionselongated on both sides of said land portion, the edges defining a trackland width and the land portion having a track center midway between theedges; overwriting two kinds of information corresponding to two kindsof light beams of different intensities by projecting onto the track thetwo kinds of light beams so as to have known beam widths and a maximumposition error between a beam center and the track center such that thewidth of a portion of the kind of light beam having lower intensitywhich exceeds a predetermined intensity above which a mark is formed onthe track is greater than the track land width by at least the maximumposition error; and providing the magneto-optic recording informationmedium with a plurality of laminated magnetic layers with verticalmagnetic anisotropy, one layer among which keeps its direction ofmagnetization constant and does not cause flux reversal at recording andreproducing.
 2. An information recording method for a magneto-opticrecording information medium as set forth in claim 1, wherein said lightbeam is a laser beam.
 3. An information recording method for amagneto-optic recording information medium as set forth in claim 1,wherein said magneto-optic recording information medium has fourlaminated magnetic layers.
 4. An information recording method for amagneto-optic recording information medium as set forth in claim 1,wherein said magneto-optic recording information medium is formed withlamination of

    ______________________________________                                        dielectric layer                                                                           SiNx             65 nm,                                          magnetic layer                                                                             Tb.sub.22 Fe.sub.69 Co.sub.9                                                                   80 nm,                                          magnetic layer                                                                             Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                        150 nm,                                          magnetic layer                                                                             Tb.sub.30 Fe.sub.84                                                                            20 nm,                                          magnetic layer                                                                             Tb.sub.30 Co.sub.70                                                                            40 nm, and                                      protective layer                                                                           SiNx             70 nm                                           ______________________________________                                    

on a substrate in that order.
 5. An information recording method for amagneto-optic information recording medium having at least one recordingtrack defined by a land portion bounded by elongated groove portionsalong both sides of the land portion and having a track center, themethod comprising the steps of:projecting onto the track a first lightbeam having a first intensity, such that a mark corresponding to thefirst intensity is formed which extends across the land portion at leastto the elongated groove portions along both sides of the land portion,the mark corresponding to the first intensity being formed in at leastone magnetic layer of a plurality of vertically anisotropic magneticlayers disposed thereon; and projecting a second light beam, with acenter disposed at a positional offset with respect to the track centerless than a known maximum, onto the track, the second light beam havinga second intensity, and the second intensity being less than the firstintensity, the second light intensity selected such that a markcorresponding to the second intensity is formed which extends across theland portion at least to the elongated groove portions along both sidesof the land portion, the mark corresponding to the second intensitybeing formed in the at least one magnetic layer.
 6. The method of claim5, wherein the first and second light beams are laser beams.
 7. Themethod of claim 5, wherein the plurality of vertically anisotropicmagnetic layers includes four magnetic layers.
 8. The method of claim 5,wherein the magneto-optic information recording medium is formed of alamination of

    ______________________________________                                        dielectric layer                                                                            SiN.sub.x    65 nm                                              magnetic layer                                                                              Tb.sub.22 Fe.sub.69 Co.sub.9                                                               80 nm                                              magnetic layer                                                                              Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                     150 nm                                             magnetic layer                                                                              Tb.sub.30 Fe.sub.84                                                                        20 nm                                              magnetic layer                                                                              Tb.sub.30 Co.sub.70                                                                        40 nm                                              protective layer                                                                            SiN.sub.x    70 nm                                              ______________________________________                                    

on a substrate in that order.
 9. An information recording method for amagneto-optic information recording medium having at least one recordingtrack defined by a land portion bounded by elongated groove portionsalong both sides of the land portion and having a track center, themethod comprising, in any order, the steps of:projecting onto the tracka first light beam having a first intensity, such that a markcorresponding to the first intensity is formed which extends across theland portion at least to the elongated groove portions along both sidesof the land portion, the mark corresponding to the first intensity beingformed in at least one magnetic layer of a plurality of verticallyanisotropic magnetic layers disposed thereon; and projecting a secondlight beam, with a center disposed at a positional offset with respectto the track center less than a known maximum, onto the track, thesecond light beam having a second intensity, such that a mark is formedwhich extends at least to the elongated groove portions along both sidesof the land portion, the mark being formed in the at least one magneticlayer.
 10. The method of claim 9, wherein the second intensity is lessthan the first intensity.
 11. The method of claim 10, wherein the firstand second light beams are laser beams.
 12. The method of claim 9,wherein the plurality of vertically anisotropic magnetic layers includesis four magnetic layers.
 13. The method of claim 9, wherein themagneto-optic information recording medium is formed of a lamination of

    ______________________________________                                        dielectric layer                                                                            SiN.sub.x    65 nm                                              magnetic layer                                                                              Tb.sub.22 Fe.sub.69 Co.sub.9                                                               80 nm                                              magnetic layer                                                                              Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                     150 nm                                             magnetic layer                                                                              Tb.sub.30 Fe.sub.84                                                                        20 nm                                              magnetic layer                                                                              Tb.sub.30 Co.sub.70                                                                        40 nm                                              protective layer                                                                            SiN.sub.x    70 nm                                              ______________________________________                                    

on a substrate in that order.
 14. An information recording method for amagneto-optic recording information medium comprising the stepsof:providing on the magneto-optic recording information medium a trackhaving a land portion, said land portion for carrying the two kinds ofinformation, and said land portion having edges defining groove portionselongated on both sides of said land portion, the edges defining a trackland width and the edges further defining a track center midway betweenthe edges; overwriting two kinds of information corresponding to twokinds of light beams of different intensities by projecting onto thetrack the two kinds of light beams so as to have known beam widths and amaximum position error between a beam center and the track center suchthat the width of a portion of the kind of light beam having lowerintensity which exceeds a predetermined intensity above which a mark isformed on the track is greater than the track land width by at least themaximum position error; and providing the magneto-optic recordinginformation medium with a plurality of laminated magnetic layers withvertical magnetic anisotropy, one layer among which keeps its directionof magnetization constant and does not cause flux reversal at recordingand reproducing and formed of a lamination of

    ______________________________________                                        dielectric layer                                                                            SiN.sub.x    65 nm                                              magnetic layer                                                                              Tb.sub.22 Fe.sub.69 Co.sub.9                                                               80 nm                                              magnetic layer                                                                              Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                     150 nm                                             magnetic layer                                                                              Tb.sub.30 Fe.sub.84                                                                        20 nm                                              magnetic layer                                                                              Tb.sub.30 Co.sub.70                                                                        40 nm                                              protective layer                                                                            SiN.sub.x    70 nm                                              ______________________________________                                    

on a substrate in that order.
 15. An information recording method for amagneto-optic information recording medium having at least one recordingtrack defined by a land portion bounded by elongated groove portionsalong both sides of the land portion and having a track center, themethod comprising the steps of:projecting onto the track a first lightbeam having a first intensity, such that a mark corresponding to thefirst intensity is formed which extends across the land portion at leastto the elongated groove portions along both sides of the land portion,the mark corresponding to the first intensity being formed in at leastone magnetic layer of a plurality of vertically anisotropic magneticlayers disposed thereon; and projecting a second light beam, with acenter disposed at a positional offset with respect to the track centerless than a known maximum, onto the track, the second light beam havinga second intensity, and the second intensity being less than the firstintensity, the second light intensity selected such that a markcorresponding to the second intensity is formed which extends across theland portion at least to the elongated groove portions along both sidesof the land portion, the mark corresponding to the second intensitybeing formed in the at least one magnetic layer and formed of alamination of

    ______________________________________                                        dielectric layer                                                                            SiN.sub.x    65 nm                                              magnetic layer                                                                              Tb.sub.22 Fe.sub.69 Co.sub.9                                                               80 nm                                              magnetic layer                                                                              Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                     150 nm                                             magnetic layer                                                                              Tb.sub.30 Fe.sub.84                                                                        20 nm                                              magnetic layer                                                                              Tb.sub.30 Co.sub.70                                                                        40 nm                                              protective layer                                                                            SiN.sub.x    70 nm                                              ______________________________________                                    

on a substrate in that order.
 16. An information recording method for amagneto-optic information recording medium having at least one recordingtrack defined by a land portion bounded by elongated groove portionsalong both sides of the land portion and having a track center, themethod comprising, in any order, the steps of:projecting onto the tracka first light beam having a first intensity, such that a markcorresponding to the first intensity is formed which extends across theland portion at least to the elongated groove portions along both sidesof the least to the elongated groove portions along both sides of theland portion, the mark corresponding to the first intensity being formedin at least one magnetic layer of a plurality of vertically anisotropicmagnetic layers disposed thereon; and projecting a second light beam,with a center disposed at a positional offset with respect to the trackcenter less than a known maximum, onto the track, the second light beamhaving a second intensity, such that a mark is formed which extends atleast to the elongated groove portions along both sides of the landportion, the mark being formed in the at least one magnetic layer andformed of a lamination of

    ______________________________________                                        dielectric layer                                                                            SiN.sub.x    65 nm                                              magnetic layer                                                                              Tb.sub.22 Fe.sub.69 Co.sub.9                                                               80 nm                                              magnetic layer                                                                              Gd.sub.8 Dy.sub.17 Fe.sub.60 Co.sub.15                                                     150 nm                                             magnetic layer                                                                              Tb.sub.30 Fe.sub.84                                                                        20 nm                                              magnetic layer                                                                              Tb.sub.30 Co.sub.70                                                                        40 nm                                              protective layer                                                                            SiN.sub.x    70 nm                                              ______________________________________                                    

on a substrate in that order.
 17. An information recording method asrecited in one of claims 1 and 14, wherein the step of overwritingfurther comprises the step of:limiting the width of the portion of thekind of light beam having lower intensity which exceeds thepredetermined intensity above which a mark is formed on the track to awidth substantially equal to the track land width plus the maximumposition error.
 18. An information recording method as recited in one ofclaims 5, 9, 15 and 16, wherein the step of projecting the second lightbeam further comprises the step of:limiting the width of the secondlight beam such that a mark is formed on the track having a widthsubstantially equal to the track land width plus the maximum positionerror.